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Sudden "nose-down" event during a normal flight in normal weather conditions
I had a flight scheduled from WAW to KIV on LOT airlines. The boarding pass told they changed the aircraft to a 737 MAX. When I saw that I've immediately remembered that whole MCAS story from 2018.
The flight went okay, just normal turbulence here and there when passing the clouds, nothing new.
However during the descent right at the border between Romania and Moldova we've slowed down and decreased the descent rate. After that we went in a heavy pitch down (the heaviest in my life, and I've flown more than a hundred times) almost lifting us up from our seats. That's when I've started to be really worried as I've thought this was the MAX model based on the boarding pass. After ≈30 seconds of this pitch down increasing the pilots started to pitch up hard, causing ≈1.8g of acceleration. After returning the plane onto horizontal flight - we've continued the flight without anything super abnormal.
I really thought that was the MAX aircraft and prayed that the pilots were briefed on how to handle it's malfunction and we wouldn't have gone into the second cycle.
However after landing I've checked that it was actually a 737-800 and now I'm reeeeeeally curios what caused that behavior. Any ideas?
Here's the flight radar link:
https://fr24.com/data/flights/lo515#2e91e2d2

How do you know that the load factor was around 1.8g? And what is the maximum descent rate shown to you in FR24?

@AdityaSharma, I've flown in small aircraft with a g-meter, so I have a general idea of it. Of course I don't have an included g-meter in my body, so that's just an approximation. Maybe could've been 1.5g. Also I don't have a premium FR24 subscription, so I don't see the decent rate

Alright, no issues!

I get that you used the ≈ symbol, but 1.8 Gs is super oddly specific.  "Roughly 2.0 based on my experiencing a 60 deg AOB turn" would be more credible.

@MichaelHall yeah, sorry for that :D I've just felt like it wasn't 2, but more than 1.5. but felt like putting 1.75 would be even more odd. The main idea is that it was very noticeably greater than my most agressive take-offs.

Unless the aircraft was close to a stall, it wouldn't be the MCAS system causing the pitch-down.  And the failure mode where one bad AoA sensor could cause erroneous activation at higher speeds has been removed.  An aggressive bid to make an altitude restriction seems like the most likely cause, followed by a realization that they'd achieved more nose-low attitude than they wanted, and an even more aggressive correction.

Well, the direct cause of such a sudden maneuver is almost certainly pilot action, rather than a system failure. Either a sudden change of autopilot settings (although the autopilot has rate limits, and outside of failure scenarios - which are incredibly rare, but possible - the maneuver should not be violent); or the pilot pushing and pulling on the control column.
Why would a pilot do that? Two possibilities that come to mind are ATC instructions ("expedite descent") or a TCAS RA. For the first case, it's not so unusual for ATC to ask an aircraft to descend quickly, to avoid spacing issues with other traffic. For the second case, automated systems onboard can detect collision threats and issue instructions to the pilots to climb or descend to avoid a collision. When this happens the pilots will maneuver strongly, in the way you described.
Unless an incident report is filed or you can somehow speak with the pilots, it will probably not be possible to figure out exactly what happened on your flight.

Thank you for the detailed answer. I've spoken to my friend who is a pilot here and has connections with the ATC - no reports were filed that day. Also it seems a bit uncanny that it happened exactly at the Romania - Moldova border. Maybe they have some restrictions on maximum altitude because of the war next door.


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Does the pilot in command need physical access to the flight controls?
Is it legal for the pilot in command to not have access to flight controls?
I can think of a few cases in which this might not be considered reckless. For example, if Alice and Bob are both pilots who are rated in the plane they are flying and have valid medical certificates, they are flying with Eve, who is not a pilot, and the plane is certified for single-pilot operation, but Bob has misplaced his pilot certificate and has not received a replacement, he cannot be PIC, but it may not be reckless for him to sit in the front left seat as pilot flying, Eve to sit in the front right seat, and Alice to sit in the back as pilot in command. Perhaps this is the only safe seating arrangement for weight and balance. Admittedly, this is a contrived scenario, but I don't see any reason why it would be unsafe. Would it be legal?

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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Does FAA 8500-7 expire?
Does FAA Form 8500-7, a report from an optometrist on a patient's vision, expire? How long after the visit to an optometrist can the vision portion of an aviation medical examination be skipped?

Obviously it expires. It would be a staggeringly stupid loophole if one could avoid vision testing for their whole career just by visiting an optometrist once.
I can't find a specific answer for how long it's good for, but the FAA considers medical records to be current if they are no more than 90 days old. I don't see why this would be any different.
On the other hand, your AME may feel differently. If you need to know, you should ask your AME before your medical appointment whether they will accept your 8500-7 in lieu of a vision test.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Is a passenger who is flying the aircraft liable for regulations that they violate?
Bob, a non-pilot, is flying as a passenger with Alice, who is a pilot. Alice is PIC, but she is letting Bob fly the plane. (He's not certificated, but he knows enough to be able to fly under supervision.) If Bob does something in violation of the FARs, my understanding is that Alice is liable because she is PIC. Does Bob have any liability?

In most cases, Alice is the only one with liability. As PIC, she is directly responsible for the operation of the airplane.
Bob could have some liability depending on the circumstances. An obvious example is if Alice attempts to take the controls back and Bob refuses, he could be criminally liable for unlawful interference with an aircraft. Alice being PIC also does not protect Bob from being liable for any criminal acts he intentionally commits with the airplane.

The latter situation would fall under §91.11.

@CarloFelicione More importantly, with 49 U.S. Code § 46504, which is a criminal statute.

That one almost certainly is going to fall onto Alice. Alice is pilot in command. She is directly responsible for, and the final authority on, the operation of that airplane, regardless of whoever was at the controls at the time.
But like anything else, there is always a situation that might fall outside of that realm.  Chris suggested the idea of a passenger attempting to interfere with a PIC or required pilot flight crewmember.  In these situations, Bob would bear responsibility under §91.11.  Another scenario might be that Alice allows Bob to take control of the airplane, Bob commences the horse around with it against Alice’s objections, which causes an incident.  I can see criminal or civil culpability landing on Bob’s shoulders for that.  Now, if the incident happened as a result of Alice’s carelessness i.e. let’s say that Bob busted bravo airspace or a restricted area because Alice was ignorant or negligent of what was going on, it’s no different than of Alice was at the controls of the aircraft herself and did that.

So Bob has no liability, because, although he is manipulating the controls, he is still a passenger, and not responsible for the flight?

He’s not PIC or serving as a required pirate crew member. The liability is solely upon Alice in the eyes of the law.  The situation is similar to a CFI, giving dual instruction to a person a board an airplane. In those kinds of flights the CFI is considered PIC and is responsible for what happens, even if the student was at the controls.

It depends on what Bob does, and what a court or the FAA administrator determines.  Liability is a legal term and is difficult to determine proactively.
One important basis for a determination would be that Alice is PIC so, according to 91.3 is "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft. "  That goes a long way towards a determination of responsibility (which is not the same as liability).
However, there are things that Bob could do to violate the FARs.  For example, if this is a part 121 operation, then FAR 121.580 prohibition on interference with crewmembers.  could apply.


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Why do most light aircraft not have AoA indicators?
Why is an angle of attack indicator not commonly included on small airplanes? Is it too expensive?

Historical inertia, mainly. AoA indicators aren't too terribly expensive to install anymore, but they were until very recently. We are now in a period where AoA indicators are fairly inexpensive and often standard in new aircraft, but most general aviation pilots are flying older aircraft and are used to flying without them.
General aviation is slow to change. Give it a few years or decades and I'm sure you'll start seeing them more and more.

One reason is just that it is hard to build as a console instrument for light aircraft. Just having an indicator on the side is easy, but having it show up in instrument cluster requires measuring an angle and then transmitting it to a dial. This is not straightforward in a repeatable way (especially where the vane part has to be exposed to weather).
The classic six pack instrument cluster is classic in part because they are instruments easy to mass produce and maintain driven by pressure alone, or using DC power of indifferent quality.
Measuring angle and remotely displaying it was traditionally done using synchros which crucially use AC power of steady frequency, normally 400hz. They were a widely used, highly reliable and well understood method of making servo systems including those on larger aircraft needing power assisted controls/autopilots. So if an aircraft already has a reliable 400hz power system for existing systems adding angle of attack sensor just means adding another angle transmitter of a type probably already widely used in the airframe, along with an repeater in the cockpit, total weight less than a kilogram and using cheap (for aviation) parts.
If the aircraft does not have a 400hz power system then adding an synchro based sensor becomes a complex power generation problem.
This couples angle of attack sensors to aircraft with larger and more complex electrical systems, which generally does not include light aircraft.
Now with compact electronic angle sensors it becomes simpler to add an angle of attack sensor for aircraft with DC only electrical systems, but as per the existing answers the baked in inertia from the earlier era still exists.

Chris's answer is spot on, but I'll add a bit.
Retro-fitting is expensive, and getting airframes included in a cert (if the airframe is no longer in production) is a calculated risk. AOA sensors are becoming standard on some new airframes but most of the GA fleet is made of of old aircraft that change hands on the used market; many of these aircraft are out of production so building and certifying new systems for them is a calculated risk/cost for manufacturers.
You are liable to find AOA sensors on new airframes like new 172's but until the FAA mandates them, adding a luxury sensor to a dated airframe is going to be a cost/benefit choice that many are not going to easily make, considering the cost of required upgrades the GA fleet has made in the last decade or so. Everyone was hit with the ADS-B out upgrade, it's getting to the point where practically flying IFR requires an IFR GPS to really make use of the NAS, and those installs don't come cheap. Even though AOA sensors are cheaper than ever, they are not required, so you are unlikely to find them widely installed.

One reason is that most of the light airplanes already have one of sorts in the stall warning.
The stall warning sensor is basically an angle of attack instrument of sorts, although with only two values. As example the Piper Cherokees has a small tab on the wing that reacts when the air starts to move "upwards. Older Cessna 172-s has a device that makes a sound when airflow changes around the wing.
--- added
Most General Aviation aeroplanes, say PA28 or C172, are made to have docile flight charecteristics. In effect this means that they will behave in a predictable and simple way even when mishandled a bit allowing the pilot plenty of time to return to safer flight conditions. In that situation an AoA meter does not really add very much to the pilot. In contrast, high-performance aircraft may have quite "angry" responses when flown. They might, perhaps with very little warning, clip towards one side whan AoA becomes to high, or perhaps enter a height eating stall. Close to ground this can be fatal. In those aircraft an AoA indication can be a life saver. I guess that most jet fighters landing on aircraft carriers comes into this category.
In some limited cases an AoA meter may be helpful in cruise allowing the pilot to optimize for lower fuel consumption. The reason is that some aircraft tend to "hang on the step" with non-optimized performance unless carefully beeing convinced otherwise. Again, the typical General Aviation aircraft does not really have this behaviour.
AoA instruments can malfunction exactly as all other instruments. The worst case would be if the instrument shows wrong values in a way that makes the pilot make otherwise unnessary mistakes. And this has actually happened in some fatal crashes (although several other factors where in effect as well).
In effect -- why add one more instrument that can malfunction when it really adds nothing in safety or performance for a typical GA airplane.


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What airplane needs the longest runway to land?
What airplane (excluding spaceplanes) requires the longest runway for a safe landing?

Can you clarify the question?  Are you wanting to compare runway length for different aircraft under identical conditions or are you interested in the longest specified length in worst-case conditions.  And is this specified min runway length or actual distance-to-stop?

FWIW most aircraft need a longer runway for takeoff than for landing (since they are heavier during takeoff)

I am guessing that you mean at maximum landing weight, maybe you can clarify just to be sure.

@Frog - It seems pretty safe to assume that they are referring to identical conditions as other comparisons would be meaningless. I would also think that it's probably for normal conditions (dry runway, 0 wind etc) but I agree that could use some clarification. It may be difficult or nearly impossible to come up with a definitive maximum, but I for one would be interested to know what are some of the typical landing distances in normal conditions for various types of airliners, cargo planes, military fighter jets, etc.

From experience with the F-84F: "If someone builds a runway all the way around the earth, Republic will build an airplane that needs every inch of it!"

Under what conditions? Landing distances are all dependent upon the airframe, landing weight, aircraft landing configuration, obstacle clearance at the runway approach end, approach speed, ambient atmospheric conditions, wind direction, field elevation and runway slope and conditions. You would have to set up some criteria here and make an evaluation based on this.

Probably some really large and heavy aircraft, hence Antonov An-225 Mriya looks like a best candidate (there are currently no flying aircraft remaining but there are intentions to build more). It needs about 3500 m and possibly more.

I'd guess the XB-70 probably needed a longer runway...


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Has any manned aircraft been hijacked electronically?
Has anyone ever taken control of a manned aircraft from the pilot by exploiting security vulnerabilities in the electronics system?

As an information security consultant this is an interesting subject for me, and I've kept my ear to the ground. No manned aircraft has ever been controlled by a hacker unless the incident has been kept out of the public domain. The only aircraft I know of that was ever hacked was when Iran used a GPS spoofing attack to fool an American RQ-170 drone into landing in Iran instead of its home base in Afghanistan. It's unlikely that would work with a manned aircraft as pilots would catch on. Even that wasn't directly manipulating the drone's systems, instead attacking the GPS signals it used to navigate. There's been some speculation that Malaysia Flight 370 was remotely taken over, there doesn't appear to be any factual basis for that.
Hackers have successfully attacked entertainment systems in the past, however in Airbus and Boeing airplane those are separated from the flight systems so the compromise of the entertainment system would not allow the compromise of the flight systems. I am not familiar with the security design of other manufacturers. There have been stories in the news saying hackers have managed to control airplanes in flight from their seats, these have not been verified and I do not consider them credible.
There are many things working against such an attack:

Remote control capability isn't built into passenger aircraft, partly because there's no need, but it's also a recognized security risk
The airplane's subsystems for flight controls and navigation are proprietary, and the protocols are not open. To successfully hack and control the airplane would require substantial knowledge on the hardware and software. Security through obscurity offers some protection in this case
Certified passenger airplanes have a high standard of testing, although as far as I know security testing isn't mandated a rigorous development process ensures a higher level of quality. Airplane's don't run on beta versions

That doesn't mean it isn't theoretically possible, so I hope manufacturers are paying attention to these.

"...in Airbus and Boeing airplane [entertainment systems] are separated from the flight systems..." There's an element here which bothers me. Boeing has in the past said that these two subsystems were airgapped /and/ firewalled: since either one of those would in principle be adequate I'm concerned that somebody was just throwing buzzwords and hoping one would stick. The fact is that automotive experience suggests that at some point somebody will connect something to both systems to "enhance the customer experience", and somebody else will then find a weakness deep inside some embedded chip.

You aren't wrong to be concerned @MarkMorganLloyd. In my line of work I've seen many wake-up calls been ignored. I have a reasonable faith in the certification system, what I would like to see is a record of professional penetration testing and security certification.

I was thinking also of this fairly recent report https://hackaday.com/2023/04/15/sufficiently-advanced-tech-has-bugs/ but it took me a while to find it. Then there was some of the original car hacking stuff which worked because one chip- for the very best of reasons- was connected to both the entertainment/environmental bus and the engine/safety bus.

Car manufacturers definitely have a way to go on security.

@MarkMorganLloyd : yes, saying they have firewalls on them is worrying. https://xkcd.com/463/ "Imagine you're at a parent-teacher conference, and the teacher reassures you that he always wears a condom while teaching. Strictly speaking, it's better than the alternative, yet someone is clearly doing their job horribly wrong."

Reason 2 seems pretty wrong to me.  The question is about manned aircraft, not airliners.  Anyone with $20,000 can buy some general aviation avionics.  There are a very large number of technicians and engineers who are very familiar with how avionics work; there is no obscurity.  Also, a quick check of Garmin's website shows some of their products are compatible with other manufacturer's avionics.  The interface protocols must not be completely closed.

@AnonymousPhysicist - a wireless temperature sensor circa 1990's would transmit to a receiver which was plugged into a 9-pin serial port on the computer, which would send not receive data. Even if someone had the full schematics and software for the receiver it seems unlikely they could figure out a way to transmit data to the receiver that could hack into the PC. This concept scaled up is GPS, VOR etc. I would hope that the connection of these receivers to the flight computers is similarly limited to the minimum required. If it's a more robust connection then it becomes vulnerable.

No, because if so it would be a famous case that all aviation enthusiasts would soon be aware of.
Assuming that it became known to the authorities that that was what happened.
(Hypothetical outlier cases that are difficult to completely rule out-- could something of that nature have happened to MH370 where little of the wreckage was ever recovered-- etc)


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Are glass cockpit or steam gauge GA aircraft safer?
All else being equal, considering the reliability of instruments, human factors, etc., is it safer to fly in a piston-single GA airplane with steam gauges or with a glass cockpit?
In other words, if I want to buy an airplane (hypothetical; I'm definitely not buying an airplane any time soon) and I see two planes that are identical except for the avionics, and safety is the only factor I'm considering in my decision, should I buy the one with a glass cockpit or with steam gauges?

Problem with traditional instruments is, you usually have only one copy of everything because the instrument panel is only so big. With glass cockpit you can spread multiple copies of all the critical sensors across the air frame, wherever the most convenient.

in https://aviation.stackexchange.com/a/84080/1289 Dean F says "some PFDs like the Dynon Skyview models have the option to switch the displays to instead represent an analog six-pack"

With rare exceptions, such as a retired fighter pilot or an ATP leisure flying in their spare time, the weakest link in a GA aircraft is overwhelmingly the pilot.
Most accidents are straight pilot error, followed by engine failure, and it's the lack of flight recorders that keeps us from learning what caused the "unknown" accidents.
Whichever display is easier for you to understand is going to be safer. Even non-certified avionics' failure rates are small compared to pilot failure in reading them.
Everything else equal, such as when learning from scratch, glass cockpits make it easier to avoid trouble. They offer GPS navigation, which is hard to misread, can display maps and traffic information, are easier to read, and sometimes include automated warnings.
That said, for pilots who already have a lifetime's experience of reading traditional gauges, it can be worth more in an emergency than the convenience of digital readouts. High stress can cause mental regression, reverting to the earliest memories of similar situations, and first training with steam gauges will transfer well to any aircraft that has them.

P.S. Technical addendum:
As far back as 1949-1953, there was a series of studies, the first involving 97 military pilots, which proved digital and single-hand dials to perform well, but dials with 2+ hands, required for e.g. altimeters, an ergonomic challenge. This has led to an increase in the use of digital counters, back then mechanical. Moving tape was deemed the best (the last design, "I", doesn't show the value's rate of change).

Glass cockpits offer a total solution. But they place a lot of information on one screen and expect the pilot to know where to look for what, how to change modes when needed, and what each mode entails. So training and regular practice with the specific PFD (primary flight display) layout used are essential to keep their reading intuitive and automatic.
Figuring out an unfamiliar PFD can take a lot of time the pilot might not have. Steam gauges aren't great, but they share a mostly-consistent design across every aircraft that has them as primary instruments.

This is a great answer.  I simply add that a modern glass cockpit has the possibility to improve safety through improved situational awareness.  Moving map GPS, traffic identification, real time radar, lightning strike detection, etc.  All have the potential to keep a pilot out of trouble.  While you could get these features on a kneeboard tablet or other add-on device, I think it is fair to consider their presence in this question.

My main takeaway is the importance of the training to actually use the instruments in simulated emergencies, over the mere technical superiority of the available instruments.  Owning the features won't save me on the day when I need them the most.

@JirkaHanika Agreed. Though I've added a technical part - there really is a significant gain to be had with glass cockpits. As long as one knows how to read and operate theirs by heart.

@JirkaHanika adding to that, interacting with the more complex features that a glass cockpit offers without prior training and/or frequent practice may lead to task fixation/cognitive lockup and contribute to loss of situation awareness. More features without training and practice = less safe


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Can you make money from a flying blog or YouTube channel with a PPL?
Is it legal for a private pilot to blog about flights, or record them and post the videos online, and monetize the content using ads?

I would say so. Check out Mojo Grip on youtube.

Related: FAA Assistant Chief Counsel for Regulations interpretation for taking photos to be sold later. This letter is discussed here.


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Has an airline passenger ever in some way prevented a crash?
Have there been any incidents in which an airliner would almost certainly have crashed had a passenger not taken some action (most likely telling a flight attendant that something didn't seem right)?

Depends if your just asking about loss of airframe crashes. The passengers of Flight 93 prevented a much larger disaster with their actions.

Not an answer, but I once jumped over an FBO counter in Iowa and grabbed the radio to wave off a guy about to take off in a small piston. He was trying to get out before a line of storms hit, and the FBO had just got slammed by a 60+ mph gust front which he would have been taking off into.

Possibly the closest to disaster because of failure of a passenger to communicate was Nationwide 723 in South Africa in 2007. The 737's engine fell off during takeoff. The pilots knew only that they lost power on the engine, and they were losing fuel and hydraulics. Meanwhile at least one passenger saw the engine fall off, but said nothing to the flight attendant who had been sent by the captain to look out the window. The flight attendant reported back to them that she couldn't see the front of the engine, which the pilots misinterpreted as meaning that the deicing nosecone had fallen off.

Its hard to prove a negative but there are cases where passengers have alerted the flight crew to things that caused a diversion or cancelation of a flight (arguably could have lead to accidents)

This fuel leak noticed by a passenger lead to a cancelation
This fuel leak noticed by a passenger lead to diversion
This passenger (who had experience) was able to fill in for an ill first officer
Joe Stiley arguably saved his own life by assuming the brace position with out instruction, before the fatal crash of Air Florida Flight 90. Being a pilot and flight instructor himself, he realized the aircraft was not moving fast enough on take off.

While these are seemingly benign examples, both fuel exhaustion and crew resource overloading has lead to crashes in other instances and you could argue, had the potential to in this situation.
Depending on exactly what your asking the passengers of United Flight 93 prevented a much larger disaster.

Your Air Florida Flight 90 link is now dead

and mind you, the plane that hit the Pentagon flew a circuit around the Capitol and was well aware that the White House, Capitol, etc. hadn't been hit. Al Qaeda painfully knew which intelligence agencies did them the most damage. My conspiracy theory is the "symbolic target" was WTC; both Washington planes were practical, to degrade US intelligence capacity.  The Pentagon was the highest priority target and/or the "lure" to get CIA and NSA to call everyone into the office... they'd have hit one or the other, and killed thousands of America's best IO's.

@Cloud I replaced the link with a link to the Wayback machine snapshot of it.

Also highly qualified pilots sometimes fly in the passenger role.
In United Airlines Flight 232, Dennis Fitch, an experienced United Airlines captain and DC-10 flight instructor, was among the passengers and volunteered to assist.
During this flight, the loss of all hydraulic fluid meant that control surfaces were inoperative. With one throttle in each hand, Fitch was able to mitigate the phugoid cycle and make rough steering adjustments.


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Will this radical design work?

My friend and I recently prototyped this radical new design for a helicopter. In this design, instead of using the main rotor to control the pitch of the helicopter, there are two other auxiliary motors at the tail rotor. This means that the main rotor doesn't tilt in any way to control the helicopter, it only controls the altitude. For the yaw, there would be another motor at the tail rotor area.
Is this even feasible? Even at a model scale?

Why two vertical tail rotors? One would surely be sufficient?

This is technically a tandom rotor https://en.wikipedia.org/wiki/Tandem_rotors with the second rotor on a long lever arm and scaled down. It can probably work in scale model but as drawn is will lack roll/lateral control.

You'll be relying entirely on the "pendulum effect" to keep it upright, it appears  (much like this -- https://www.youtube.com/watch?v=f4cAylbWvmU )

Roll control is missing. There is no pendulum effect with fixed rotors.

@quietflyer pendulum effect can only happen if the connection between the lifting element and body is flexible. If the axis is rigid, it doesn't matter if the rotor is above at or below the body. If the connection is flexible, you now have to manage the tilt of the rotor disc directly, and presto, you have Bell's teetering rotor system.

Perhaps one of these                     might interest you.  Who says you could not put an electric motor in the rotor for vertical take-off, then recover energy from the rotor once forward flight was achieved.

Not as drawn.  There is a fundamental problem that would make directional flight impossible.  It looks to me like one of your design goals is to simplify the main rotor hub by eliminating the complexity of the cyclic mechanism by having a fixed hub, and you modulate only rotor RPM.  This helicopter could theoretically hover, but once in directional flight (presumably forward) an entirely fixed main rotor hub without any cyclic mechanism would have no means to compensate for the difference in lift produced by the advancing and retreating blades.  It will roll into the retreating blade.

@U_flow -- see link in my comment -- I've been threatening to ask an ASE question about this topic for years, maybe it's time--

@quietflyer a common misconception. If you draw the situation up, you will quickly realize that there is no pendulum effect for fixed rotors

Do some research into cyclic pitch and why its needed.  This was the mistake made by  many of the early would-be inventors of the helicopter.

It should be feasible (with some modifications). And unfortunately is not radical nor new: Any RC helicopter toy without swashplate is controlled in a similar way, like the one in this picture (source):

Here the two contra-rotating main rotors produce the thrust to lift the helicopter and they balance their own torques.
To make the thrust pointing forward and give the helicopter a forward speed, the small rotor on the tail is activated so that it generates an upward thrust: this produces a nose-down pitch which makes the helicopter and the main thrust tilt forward, producing therefore also a forward force. If the rotor on the tail is activated to generate an downward thrust, it makes the helicopter and the main thrust tilt backward producing this time a backward force. This part is similar to your idea.
Yaw is controlled making the two main rotors rotate with a slightly different speed. In your case the yaw is controlled via a third rotor, much like a conventional helicopter.
Obviously there's no means to tilt the helicopter with its thrust to the right or left, so lateral movements are not possible.
As also pointed out in some comments, stability might be an issue. Thanks to the rotors on the tail, you might be able not only to manoeuvre but also to keep it stabilised in yaw and pitch but only if its own proper movements around those axes are not faster than your reflexes. Anyway, as already said, in roll there's no way you can control and stabilise it. A mechanical stabilising bar like the one in the picture is therefore necessary.
Another problem is the dissymmetry of lift that would make the helicopter tip over as soon as it moves somewhere horizontally. To avoid this, the blade shouldn't be rigidly connected to the rotor head but free to flap either via an hinge or making the blade's root soft.
So, taking into account these modifications, at the end you obtain an RC helicopter just like the one in the picture I posted :)

Does this question, and associated answers, suggest that the stability dynamics of the helicopter in your picture are considerably different than the one in the question?  https://aviation.stackexchange.com/questions/64969/how-does-this-rc-helicopter-keep-itself-upright?rq=1

@quietflyer: for sure not, the same stabilising bar might be needed, but the general idea isn't something new and should be feasible.

I’d recommend being more specific in your answer.  The design you show is feasible because of the unique characteristics of counter-rotation, which is absent in the concept.  As I mentioned in another comment, the counter-rotating blades don’t just simplify the design by eliminating a tail-rotor gearbox;  They simplify the design by countering asymmetric lift.  Without counter-rotation, you have two problems to solve, not just torque.

@MaxR: you're right, I actually wanted to expand that part of my answer but it's always a bit difficult to understand when it gets too long, technical and boring... Maybe I'll link some other answers dealing with those topics.

@sophit just to be clear. The design the question poses is not feasible. It possesses no roll stability, an no means to counteract. I am sure that you are aware, that this is due to the fixed propeller. The design which you link has fly bars and flexible linking of the blades which is part of its stability concept. The proposed design lacks these features. I propose that you modify your answer accordingly. Because your first statement is wrong. The proposed design is not feasible.

@U_flow: thanks for your suggestions, now the answer should be clearer

@MaxR: thanks for your suggestions, now the answer should be clearer

The Wikipedia article about the "dissymmetry of lift" seems to have several issues, to the extent that I would not cite it here. The flapping and lead-lag hinges on a rotor head are for mechanical reasons (avoid overload and failure) and certainly not to compensate for asymmetric lift. Flapping / lead lag motions are anyway too small and hence too slow to have a significant influence.

@CarlBerger: I couldn't find anything better... and at least the pictures are correct ;)


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What determines the active runway and is crosswind or headwind with crosswind better?
Today I read the METAR for Mumbai airport (VABB) and it goes like this
VABB 180730Z 23007KT 3000 HZ NSC 28/14 Q1013 NOSIG

Here the wind is 07 knots from 230, so if they used the main runway number 27 that is primarily used, they would have a headwind component of 5.4 knots and crosswind of 4.5 knots.
Instead, from this morning (5:30 UTC approx) onwards they are using runway 32, which would result in all the takeoffs and landings having a straight 7-knot crosswind.
What could be some reasons for them using runway 32 instead of 27?
I don't think any runway maintenance is going on for runway 27, so we can rule that out.

A 7 knot crosswind component is entirely inconsequential to airline operations.

See also the answers to this question.

I would have expected them to prefer 09/27, which is the longer runway.

There are many things that go into the selection of which runway to use beyond the crosswind component. Those things include but are not limited to:
Noise Abatements: Some airports have noise abatement procedures with the local area preventing overflight at certain times. Runways may be dictated by that when possible.
ATC: Controllers may chose a particular runway for ground or air traffic flow reasons.
Scheduled Work: Runways get a lot of hard abuse and need to be inspected and maintained, its possible runways were switched (and one closed) for routine work like inspections for debris, light bulb changes, painting, sealing or paving.
Length: In your case they actually moved to the shorter runway but in many cases runways may be changed to allow for larger aircraft.
Wind: All aircraft can land in a cross wind up to some practical limit that limit varies by aircraft and testing but 7Kts is pretty low across the board. ATC may change runways when the cross wind component exceeds limits for the aircrafts in question.

Yeah, I think there could be some work, it's not noise abatement because it doesn't exactly happen regularly.


text:
Why do you need to provide your arrival airport when you close a VFR flight plan?
I file VFR flight plans all the time, now that 1800wxbrief.com makes it so easy to open and close them.
Opening is easy, just click the activate button, but when it's time to close the flight plan, you have to type in your arrival airport.  Of what value is that particular piece of information to FSS?  Is there a historical reason why they request it?

I'm guessing if your arrival airport is different from your planned destination, they may need to advice your planned destination that you are no longer coming

In the past, when run by the feds, the FSS responsible for the destination airport held the responsibility for making phone calls and alerting SAR.  So if you wanted to cancel a flight plan, it was essential to determine what FSS your plan needed to be cancelled at.  That was established by the destination airport.

My understanding is that providing multiple pieces of information related to your flight plan when communicating is to ensure that the correct flight plan is being manipulated.
It seems odd that it would be required on an electronic format, but what if your N-number is N1234RF and a person closing the flight plan types N1234EF?
There is potential to close the wrong flight plan.  Now the likelihood of both of those N-numbers having an active flight plan to the same destination and having someone fat-finger it at the same time is much less likely, obviously.
Also, "if you are flying to multiple airports this function provides a chance to confirm which of the flight plans you are using. Ex. a student pilot flying from their Home airport to airport A, taking a break then flying onto airport B before flying back home." - Dawn Breaker
So it is just a cross-reference for accuracy.

I would add that if you are flying to multiple airports this function provides a chance to confirm which of the flight plans you are using.  Ex. a student pilot flying from their Home airport to airport A, taking a break then flying onto airport B before flying back home.

As a matter of trivia, I do not think N123JRF meets the US criteria for an N number.  The limit is two alphabetics, unless the rules have changed.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Other than training and some landings, do pilots ever stall on purpose?
Other than in training/practice and some landings, do pilots ever intentionally stall?

Not a large group, but Functional Check Flight pilots will typically perform a series of stalls in an airplane in various configurations before initial delivery and after major maintenance. If it stalls at other than the expected speeds, or if one wing stalls before the other, adjustments are made and the FCF is repeated.
Stalls are just one of many, many things that get checked before initial delivery; how much gets checked after major maintenance depends on what was changed out.

I think I recall a DC-8 crash over West Virginia where they were doing this.

@PresidentJamesK.Polk  That's entirely possible (though probably not during your term in office).  FCF's are performed on aircraft that are supposed to be all fixed, but sometimes aren't, and so they do have an element of risk to them above what would be accepted in normal airline flying.  That risk is partially offset by having specially trained pilots performing them, and of course not having passengers on board, but turning off systems, shutting down & restarting engines, performing stalls, and so on will always entail some amount of risk beyond the norm.

Here is the NTSB report.  Elsewhere I found that the pilot flying was Captain Lemming, a very unfortunate name for a pilot. Another bizarre one-in-billion: The sister of one of the fatalities on the flight was killed in another plane crash going to his funeral.

Lots of pilots do stalls for fun, practice, something to do, whatever, and if the plane is certified for spins, those too. In Canada, spins are part of basic pilot training.
The main safety issue with doing stalls is altitude. You want to be at least 3000 ft agl, in airspace that isn't controlled, or crowded, and after checking for airplanes below you. There are various precautions.
Most aircraft can be stalled, then cross your arms and do nothing, and it will more or less recover on its own (you'll have to intervene to manage the dive as it recovers). In fact most airplanes will recover from spins on their own if you just take your hands off the controls after the spin starts.

Gliders can recover from stalls even quicker, sometimes in as little as 50 meters (although it's best to have a lot more reserve). And gliders often fly pretty close to their stall speeds anyway when in a really tight thermal.

Yeah I done hours of thermalling in a 1-26, where you thermal right down in the pre-stall buffet. Some of the high performance stuff is a bit less forgiving tho and I avoid flying directly below them in thermals.


text:
Are passengers required to obey pilots' commands?
If the pilot in command of a GA aircraft tells a passenger to do or not do something, is the passenger legally obligated to obey the pilot? For example, if the pilot tells a passenger "Stop talking" (presumably because the passenger is being distracting), is the passenger required to stop?
Assume that obeying the pilot is legal (i.e. the pilot isn't telling the passenger to commit a crime), no contracts or other prior agreements have been made, and the passenger is not required to obey the pilot for other reasons (e.g. the passenger is not the pilot's minor child).

Iirc in europe  aviation laws generally define the PIC as the person responsible for the safe execution of the flight. To achieve this, the PIC has virtually unlimited powers, so if safety was involved, yes, in most european jurisdictions the passenger would have to obey the PIC

I think this falls under Mom Law, as in "Don't make me turn this plane around!"

There is no such general requirement. However, passengers are forbidden from interfering with crewmember duties, per 91.11:

No person may assault, threaten, intimidate, or interfere with a crewmember in the performance of the crewmember's duties aboard an aircraft being operated.

So in practice a passenger is required to comply with many instructions, where failure to comply would interfere with the PIC's ability to fly safely.
"Stop talking because you are distracting me during a critical phase of flight" would likely be considered such an instruction. (Though the pilot may be better served by just turning off the intercom). "Stop slouching, bad posture offends me" would probably not be.
Note also that disobeying this law is not a crime. The FAA can levy civil penalties (e.g. fines) against passengers who ignore crewmember orders, but they can't send them to jail or anything. There is a criminal prohibition against physically interfering with crewmember duties in 49 CFR 46504:

An individual on an aircraft in the special aircraft jurisdiction of the United States who, by assaulting or intimidating a flight crew member or flight attendant of the aircraft, interferes with the performance of the duties of the member or attendant or lessens the ability of the member or attendant to perform those duties, or attempts or conspires to do such an act, shall be fined under title 18, imprisoned for not more than 20 years, or both. However, if a dangerous weapon is used in assaulting or intimidating the member or attendant, the individual shall be imprisoned for any term of years or for life.

But this does not apply to merely disobeying a instruction.

I'm going to guess that there is also a law against endangering a plane, such as trying to open the door of a pressurized plane, even if you don't intimidate a member of the flight crew doing so.

@DJClayworth I'm not aware of any such law specific to aircraft. But endangering people is a crime regardless of whether you are on an aircraft or not.


text:
How often do airline pilots actually have to avoid other aircraft that ATC did not tell them about at cruise altitude?
I know any pilot flying in VMC, whether under VFR or IFR, must "see and avoid." How often do airline pilots actually "see" and have to "avoid" other traffic at cruise altitude without being told about the traffic by ATC? Can it happen without someone doing something wrong?

It's possible if someone departs from a clearance, but that's what TCAS is for.  The vertical separation is only 1000 ft at the FLs above 280, and because of GPS, everybody is exactly on the airway centerline, so when someone passes above or below on your airway, they pass precisely overhead or underneath, 1000 ft above/below. They look like they are coming straight at you until they are a couple miles out.

Above FL180, basically never. Below, just like any other VFR pilot
Expanding on 757toga's answer, in the US there are altitudes above which it is not legal to fly except under IFR. At those altitudes, there should never be anyone. However, that leaves flights over international waters as well as flights below those altitudes.
Below 18000', there is no positive control of the airspace. The FAA politely asks that VFR pilots cruise at altitudes ending in 500', e.g. 3500', 10500, 14500', etc... However, the request is not a requirement, in that not everyone in the sky is is cruising. There are many, many users of the sky, such as gliders, aerobatics, balloons which would not be expected to be in level flight.
So IFR flights below FL180 still need to aggressively practice see-and-avoid. Airlines will fly at those altitudes often enough when coming into and out of airports, so they will need to see-and-avoid just like a normal VFR pilot.
The only time an IFR pilot can be sure there's no one at a sub-FL180 altitude is when flying in a cloud and thus knowing there are no VFR pilots around.
ATC will provide guidance if there are transponder or radar blips, but there is no universal transponder requirement and so many planes are invisible to ATC.
That being said, the sky is a very, very, very empty place. The number of times I've had to see and avoid, as opposed to simply see is... 0? (I'm not counting flying in a gaggle with other glider pilots.) I imagine most pilots are in a similar boat.

14 CFR 91.159 is not phrased as a request...

The only times that I have had to see and avoid another airplane were within Alert areas for high amount of flight training. Airplanes in those areas usually do a lot more climbing, descending, and turning due to the nature of operations.

"Below 18000', there is no positive control of the airspace." -> What about class B airspace?

@Bianfable that's a fair point, but those airspaces are few and far between.

@randomhead, sure, and I'm assuming you were one of the downvoters. Please note that the 91.159 is only applicable to level cruising flight.  I've updated my answer to make it more clear how 91.159 is not applicable to the OP's question. We are frequently up and down the airspace within the mode-C veil, in gliders and aerobatic experimentals with neither ADBS nor transponders.

@downvoters in general, I think you should reconsider your downvote. Pilots who see the airspace as only IFR cruise or VFR cruise are some of the biggest threats to users who are pure VFR. It's galling that there are so many of us who seemingly never look outside our cockpits, because too many of us feel 91.159 and ADSB gives us invincibility.

Well, the question was about airliners at cruise altitude, which tends to imply above 18,000' MSL.  So the answer was broader than the question, but not in any way that was unclear or confusing.  I strongly agree w/ a lot of the content in answer, and in comment immediately above.  Shame about all the dv's.  Rephrase to delete "politely asks" but keep the other content and maybe they'll come to their senses and reconsider.

There's a new question here somewhere in the making, what is the definition of "cruise" anyway, on a long XC flight if I choose a continuous steady climb to the midpoint and then a continuous descent, flying VFR below 18,000', am I violating any reg? How low would my climb or descent rate have to fall before I were considered to be "cruising"?  Someone ought to ask that question.

@quietflyer that's an excellent point, and why I had the "politely ask" phrase. 91.159 mentions level cruise only, so if you are climbing and descending you are not violating any regs, nor even, I would argue, behaving inappropriately. AFAICT, 91.159 is toothless and probably only can be enforced as part of a broader 91.13 administrative action.

Wow, still collecting downvotes. Literally spoke about this topic with a glider DPE a week ago and we both concluded that there is no requirement for aircraft to be at those altitudes. People, please keep your eyes open for the many, many users of the space who are not at all visible to ATC. Just two weeks ago, I was thermalling at 7k' with Spirit jets passing below at 5k'...


text:
Why are there so few recreational pilots?
There are far fewer holders of recreational pilot certificates than any other class. Why?

As you point out, there are very few recreational pilots out there right now. I think out of the some 600,000 licensed pilots in the United States only about 500 or so recreational pilot certificates have ever been issued. I can’t speak on the history of that particular pilot certificate from the FAA.  For practical purposes, an RPL’s only use is for a student pilot to solo in an airplane, but is not interested in pursuing additional pilot training; he/she only wants to fly this one airplane around a local airfield on recreational flights under visual flight rules. Additional privileges for a recreational pilot certificate can be obtained with additional training and instructor sign-offs, though you’re always hamstrung to flying light airplanes in a limited capacity under VFR. Most people, in seeing what you get for recreational pilot certificate, choose instead to pursue additional training as a student pilot and obtain at least a private pilot certificate.
As to different medical requirements to be a recreational pilot, there are none as opposed to those needed for private pilot.

I can’t quote the exact source, but judging by the FAA’s current data on airmen certification the 500 number seems pretty accurate.  https://www.faa.gov/data_research/aviation_data_statistics/civil_airmen_statistics/2022

Those are active pilots. My comment of  500 or so applies to all RPLs issued over the entire history of the certificate

500 vs 79 is almost an order of magnitude difference, but it's not really significant for the question. Either is an extremely small number compared to the number of SPCs, PPCs, CPCs, or ATPCs.

The only benefit of a recreational pilot's license is slightly fewer training hours required:

Only 15 dual hours required instead of 20
Only 30 total hours required instead of 40
Only 3 solo hours required instead of 10
No night training required
Reduced cross-country requirements
No instrument training

Note that these are reduced minima, and most students take more than the minimum hours. The minimum being 30 hours doesn't help much if you take 50 hours anyway.
In return, a recreational pilot is not allowed to:

carry more than one passenger
fly a plane certificated for more than 4 passengers
fly a plane with more than 180 HP
fly a plane with retractable landing gear
fly over 10,000 feet (unless under 2000 AGL)
fly at night
fly in visibility less than 3 miles
fly over clouds
fly a multiengine airplane
fly more than 50 nautical miles from your home airport
fly in airspace that requires communication with ATC
fly for compensation or hire
tow anything
fly outside the United States
act as a required crewmember when more than one pilot is required (this means no acting as a safety pilot)
do preventive maintenance on an airplane

Also if recreational pilots go 180 days without flying, they must fly with an instructor to reestablish currency.
Some (not all!) of these restrictions can be removed by receiving additional training and receiving an endorsement. But at that point you may as well have done the PPL in the first place. Getting the RPL first and then transitioning to the PPL is more expensive since it requires an extra knowledge test and checkride.
Meanwhile a sport pilot license has even less training required and hardly any more restrictions. Additionally, you don't need a third-class medical, which is a big benefit for some pilots.
In some ways, the recreational pilot license is even more restrictive than the sport pilot license. For instance, when operating under the RPL without a cross-country endorsement, a pilot must receive a separate endorsement for each departure airport.

What are the advantages of an RPL?

somewhat lower cost
lower medical requirements

What are the disadvantages?

massive restrictions on what you can fly
massive restrictions on where you can fly
massive restrictions on when you can fly
no upgrade path to other licenses
fewer aircraft out there to rent
aircraft of far lower specs, I could have gone for an LPA when learning for my PPL for example but there were none that could take my weight plus that of my instructor.

So for a few small benefits you get a lot of restrictions.
Effectively the sole reason to go for an RPL is if you can't meet the requirements for a PPL medical but do want to fly. Most people who don't meet the requirements for a PPL medical are going to be responsible enough to not risk flying (I sure am, if I'd got my medical I'd by now have handed it in).

Thank you! Does "no upgrade path to other licenses" mean that once you're had an RPL, you can never get another certificate?

No.  It just means that you must meet the aeronautical requirements of a PPL before you can upgrade.  I would not have included that line in the list.

@Someone no, it means you'd have to start from scratch. You can't just go to the FAA or EASA and get your license converted into a PPL. You also can't add a multi engine, complex, etc. endorsement

What lower medical requirements? Recreational pilots still need a 3rd class medical or BasicMed.

@jwenting do the hours and training for the RPL count towards the PPL?

Yes, in order to exercise privileges of a recreational pilot, you will, at least at some point in your life post July 14, 2006, held at least a third class medical certificate. See §61.23.


text:
What class are amphibious aircraft?
Are amphibious airplanes considered land or sea planes for pilot certification? Can an ASEL-only pilot fly an amphibious single-engine plane if (s)he only takes off and lands on land? Can an ASEL-only pilot take off from the left seat, then let the ASES-only pilot in the right seat take over and alight on water?

Amphibious aircraft are in the same class as seaplanes. There are no single-engine or multi-engine amphibious ratings, it's either land or sea, and if the aircraft can land in water you need the seaplane rating, regardless of whether it also has landing gear and you only ever operate from land.
https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/seaplane_handbook/media/faa-h-8083-23-2.pdf

Do you have a citation for this? I've had difficulty finding any reliable information. In particular, I'm a bit skeptical that a pilot with only a seaplane rating is allowed to operate an amphibious plane if they are operating only from land.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/seaplane_handbook/media/faa-h-8083-23-2.pdf
You can verify for yourself there is no amphibious rating or endorsement. If you have a seaplane rating and want to fly an amphibious aircraft you only need a proficiency check regardless if you want to fly from water or land.

I'm aware that there is no amphibious rating. That doesn't necessarily imply that a seaplane rating is adequate for operating from land. The handbook you linked mentions amphibious aircraft only briefly and doesn't say anything one way or the other about regulations regarding them.

On the other answer you say "This answer assumes that a seaplane can magically become a non-seaplane if amphib floats are installed and can be operated by someone who does not have a rating to operate an aircraft certified as a seaplane. I highly doubt any FAA ramp inspector will let this pass." But by your logic you could make a landplane a non-landplane just by slapping some amphibious floats on it and it can be operated by someone who does not have the rating to operate a landplane. How is that any different?

@Chris Without an STC, what you would be producing would be an experimental aircraft, and flying it without the experimental a/w certificate would be illegal. You can't just "slap" things like that on type certified aircraft.


text:
Can a pilot with a PPL be reimbursed by an employer for fuel?
If someone with a PPL has to travel for work, and they decide to take their plane, can they be reimbursed by their employer for fuel?

This question seems to be asked periodically online, often without complete consensus, especially given differences in each unique scenario. The short answer is yes under certain restrictive conditions.
The relevant regulation is 14 CFR 61.113 in particular 14 CFR 61.113(b) which states:

(b) A private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if:
(1) The flight is only incidental to that business or employment; and
(2) The aircraft does not carry passengers or property for compensation or hire.

These two requirements should be fairly straightforward, although the determination of what is considered incidental can get a bit murky. But, if your employer is asking you to transport several of your colleagues and company property that is needed at a conference, for example, this would be a violation.
The FAA clarified some of this in the Mangiamele Letter which clarifies 14 CFR 61.113(b) in the paragraph below:

Section 61.113(a) states, in pertinent part, that a private pilot may not, for compensation or hire, act as pilot in command of an aircraft. An exception to that section states that a private pilot may, for compensation or hire, act as pilot in command of an aircraft in connection with any business or employment if the flight is only incidental to that business or employment and if the aircraft does not carry passengers or property for compensation or hire. Thus, in this scenario, where you are only transporting yourself to the business meeting, you may be compensated for the expense of the flight.

The letter also clarifies some other situations (e.g. when passengers are on board).

What if I'm also carrying a business laptop?

IANAL and IANAP, but it seems reasonable, @Someone, that you would be allowed to transport yourself and personal business needs to that meeting and have the company pay the fuel bill. The difference (to me) is that you're carrying your personal needs, not items needed by others. If you're carrying 30 laptops for demonstrations and coworkers, no, if your carrying your own work-issued laptop, you're good. (Again, not a lawyer or pilot, just attempting to apply logic & reason to what I've read here.)


text:
Why would a pilot with a current medical use BasicMed?
A pilot whose certificate I just looked up has both a valid second class medical and a BasicMed CMEC date listed. Why would a pilot with a valid medical use BasicMed?

How do you look up other pilot's medical certificates, and how is this not a HIPPA violation?

@MichaelHall it seems easy to look that up in the FAA database.

Interesting... this seems a bit private to be putting in a searchable database, especially without the Pilot Cert # as a required field.

@MichaelHall yeah, it just comes up when you search for their pilot certificate. It's not kept private at all. Apparently the certificate number and date of birth are the only things shown on the plastic certificate but not online.

@Someone Pilots can also request that their address not be released, and then it will not show the address either.

@MichaelHall the FAA is not a healthcare provider, and thus HIPAA does not apply to it.

If you're going to, you know, throw tons of metal around in the air above millions of people, "privacy" seems a weird concept!

Any number of reasons.
It could be that their medical expired and they were operating under BasicMed until they could renew it. It could be that they are planning not to renew their medical and just operate under BasicMed once it expires. It could be that they want to still be good to fly if their medical is deferred in the future. It could even be that they just want to be covered in case they misplace their medical and want to keep flying until the replacement arrives.


text:
What happens after crashing in a commercial flight simulator?
If you crash in a commercial flight simulator (the type used to train airline pilots), what happens? Do you get a pop-up window in front of you saying "You have crashed"? Does it just show the last scene from before the crash until the simulation is reset? Does it just turn off?

Answered here for at least one system https://aviation.stackexchange.com/a/88461/60886, and a reason for not actually crashing https://aviation.stackexchange.com/q/87283/60886

You will survive!

It probably says 'go talk to your training captain'

Tom Scott crashed a B737MAX in a professional simulator: https://www.youtube.com/watch?v=YaOvtL6qYpc (from 16:30) and the screen went red...

Personally I believe you have to pay the drinks. :-)

Your mind dies as in the Matrix. Tough but fair -- this is why pilots used to make the big bucks.

In the B-52 WSTs a loud klaxon went off in the building, to embarrass you.

After the simulator crashes, you fix it by turning it off and back on again.

All that happens (in the Level D CRJ machine I trained in) is the visuals black out, there is a sort of crash sound effect, the machine freezes in place momentarily, then returns to its level docking position. The instructor has to do a reset procedure at his controls to get it back in business.
When doing V1 cuts (engine failure during rotation) for the first time, it's not uncommon for pilots new to swept wing jets to crash the rig, because with swept wings the roll rate generated by a large yaw, that is uncorrected with rudder in time, will have you in a 45 o bank before you know it and the wing tip will hit the ground.

Airline pilots can train in a variety of certified simulators but you are likely thinking of the full motion level D simulators. In some cases its just some bad graphics of bouncing as seen here or other unrealistic crash dynamics.
Here is some info on what happens if a pilot does it during real ATP training.

Yes infact you do get a popup window of the type you mention on the instructors panel.
Depending on the severity of the crash the visual and  motion may freeze or continue and mostly need some sort of reset.


text:
Are there certification requirements for software that is intended to be used in flight, but runs on uncertified hardware and is not safety-critical?
If I wrote a navigation app for pilots, designed it to run on non-built-in tablets, and included a disclaimer and warning not to rely on it (I would hire a lawyer for this part), would that be legal, and would my software have to be certified by some process?

Note that in general, you cannot lawyer away rules and regulations. If you write an app to do X and try to disclaim its use for purpose X, you have another problem, namely that your product isn't fit for purpose. You could hire a lawyer to give you an informed opinion whether your product would be compatible with FAA regulations, but expect to pay for that.

@MSalters can't you also disclaim the warranty of fitness for purpose, as many open source licenses do? Of course, add too many disclaimers and people likely won't buy your software, but I don't think there's a legal issue. (I will definitely hire a lawyer before I make any decisions regarding this issue.)

IANAL and I don't have the slightest clue how this works in the US, but at least in several EU countries you can't sell a screwdriver with a disclaimer saying it is not to be used for driving screws, but you could give it away for free. I suspect that might be what makes it work for free software.

@Someone: Open Source is different; the license grants an exception to copyright. Typically use of the software isn't even covered by the license (e.g. GPL), only copying the software. Hence such a license needs to make clear what it does cover (copyright), and what it doesn't cover (warranty).

Tablets and other portable devices are not part of the aircraft's type certificate, so they are not required to be certified.  Therefore, neither is the software.
For equipment permanently installed in aircraft the rules are different.

As I understand it, airlines now provide various operational manuals - checklists, etc. - on tablets for use before and during flights in order to save on the cost and weight of paper. Do those need technical certification? Or do they just have to sign off that "this is an exact duplicate of the paper version"?

@manassehkatz-Moving2Codidact: On a related note, are there requirements regarding the quality of paper used for paper manuals?  Manuals printed on thinner paper might weigh only half as much as the same number of pages printed on thicker paper, but be more likely to be accidentally rendered illegible.

@manassehkatz-Moving2Codidact, good question, I may add something about EFBs here later...  Supercat, I think that's an unrelated question.  Ask separately if you like, but I wouldn't know how to answer it.

@MichaelHall: If there are specifications regarding the durability of manuals, that would seem like an explicit acknowledgment that they are to be treated as safetly-critical flight equipment.

@supercat, I'm not completely disagreeing with the premise of your question and comment, but in all my decades I have never heard of paper publications referred to as "flight equipment".  Nor have I come across any specification for durability.  They are replaced at regular intervals as new versions come out, and if you tear a chart or drip sweat on your approach plate you simple grab a new one whenever you prepare for your next flight.  It's a consumable paper product - that's a far cry from certified hardware.

@supercat are aircraft manuals long enough that their weight matters‽

Like any other "physical" component of an aircraft, also software must show compliance to airworthiness regulations in order for it to get approved by certification authorities like FAA and EASA.
The defacto standard used worldwide to show that software complies with these regulations is called DO-178C. In particular, FAA and EASA define it an "acceptable means, but not the only means, for showing compliance with the applicable airworthiness regulations for the software aspects of airborne systems and equipment certification".
DO-178C is basically the framework within which both industry and certification authorities moves to develop and demonstrate (the former) and approve (the latter) avionics' safety.
Also other safety-critical industries like railroad, medicine, nuclear power and so on use very similar standards of certification.
DO-178C defines five so-called "Development Assurance Levels" i.e. five levels of software criticality according to how much dangerous the piece of software under scrutiny is. In particular, the criticality can be (from Wikipedia):

Catastrophic - Failure may cause deaths, usually with loss of the airplane.
Hazardous - Failure has a large negative impact on safety or performance, or reduces the ability of the crew to operate the aircraft due to physical distress or a higher workload, or causes serious or fatal injuries among the passengers.
Major - Failure significantly reduces the safety margin or significantly increases crew workload. May result in passenger discomfort (or even minor injuries).
Minor - Failure slightly reduces the safety margin or slightly increases crew workload. Examples might include causing passenger inconvenience or a routine flight plan change.
No Effect - Failure has no impact on safety, aircraft operation, or crew workload.

Now, how thorough the development and the approval path of the software is, directly depends on which criticality level the software posses. In particular, software belonging to the fifth and last category i.e. software which poses "no effect" on the airplane's safety, does not need to show any compliance with airworthiness regulations.

Are there certification requirements for software that is intended to be used in flight, but runs on uncertified hardware and is not safety-critical?

So, anything running on a personal tablet/pc/smartphone must not be certified for the simple reason that it is not a threat for the flight's safety: you may well forget it at home and fully be able to safely fly anyway.
Anyway, if the piece of software running on the tablet becomes safety critical, i.e. if it belongs to one of the first four levels previously defined, then not only the app but also the operating system as well as the hardware would have all to be certified.

An example of something with no effect would be a video camera used to film the flight. Any navigation app would be at least minor (increased workload), right?

It increases workload if it breaks.

Can you imagine a navigation app which is not needed to fly and does not increase workload if it fails?

uh, the usual definition? a computer program that one might run on a tablet in order to navigate?

@user253751: well as already said, if the app is necessary to fly and falls inside one of the first 4 definitions of criticality, then it must be certified together with the hardware it runs on and the operating system. That I know, neither Android nor iOS nor windows mobile are certified so if your app run on one of those OSs then it is either not critical or used illegally.

Can you imagine any kind of navigation app whose failure would not increase workload? perhaps route planning prior to actual flight. If you cannot, then you can exclude the possibility that the OP's navigation app's failure would not increase workload.

@user253751: if the app is used before (i.e. not during) the flight then it is not flight critical. But most of all: doe this app count as avionic? P.s. I clean a bit the comments before they get migrated to chat

There are plenty of (ppl) pilots that use Google Maps on a phone or tablet as an add-on. Not for primary navigation (I hope) but in its terrain view it can really help for visual orientation and/or to point out landmarks to passengers.

@user253751: "Not for primary navigation (I hope)" then we hope the same  I suppose that if an accident happens and it can be demonstrated that the pilot was distracted by such apps then it won't be funny for the pilot... Everything that does not belong to avionics should be left either on ground or to the passengers. Piloting (even biking) needs concentration.


text:
What are the visual acuity requirements for private pilots?
I have 20/30 vision in one eye, 20/50 in the other. With glasses, I get 20/20 in both. What are the visual acuity requirements for a PPL? Presumably (hopefully?) someone with my visual acuity can't fly without glasses? (I definitely wouldn't even drive a car, let alone fly a plane, without glasses, even if it wasn't legally required. I could probably see the instruments in a plane fine, and I could see outside well enough to avoid hitting another plane, but I would probably have a hard time finding a runway to land on.)

The FAA has pretty straight-forward rules for vision acuity for 3rd class medical certificates, which (unless you're flying under Basic Med) is required to exercise private pilot privileges:

Near Vision: 20/40 or better in each eye separately (Snellen equivalent), with or without correction, as measured at 16 inches.
Distant Vision: 20/40 or better in each eye separately, with or without correction.

If you're correctable to 20/20, then you'll pass the vision test just fine (unless there are other issues beyond what you've described).  If you require glasses in order to pass, your medical certificate will have a note to the effect that you have to wear (or, "have available" in many cases) glasses while flying; that's very common, especially among pilots older than about 45, which is when presbyopia typically starts to set in.
Even 20/20 isn't strictly necessary; if you have 20/25 distant vision and good near vision, there's no need for glasses. The flight surgeon can tell you the exact limits, but since you're correctable to 20/20, that answers the specific question for your case.

Thank you! I do have astigmatism, but it's also correctable with glasses.

@Someone I can imagine astigmatism to be overwhelming for commercial pilots (nightflying near busy airports involves all kinds of lights), but as small-time flyer you should be fine.

@Mast I probably wouldn't fly at night, considering that it's hard to drive at night (although I can do it).

The old saying is that if you can walk to the doctor's office unaided and read the name written on the office door, you'll probably pass the third class medical exam.


text:
Is "Air Force One" used as an ATC call sign?
When the President is on an Air Force aircraft, is "Air Force One" the actual call sign used on the radio with ATC?

Very well then...

According to an airforce fact sheet about the airforce one fleet

The presidential air transport fleet consists of two specially
configured Boeing 747-200B's — tail numbers 28000 and 29000 — with the
Air Force designation VC-25. When the president is aboard either
aircraft, or any Air Force aircraft, the radio call sign is "Air Force
One."

And the answers to another Q  has other relevant info - like why it isn't designated Heavy

Yes.
From Wikipedia:

Air Force One is the official air traffic control designated call sign for a United States Air Force aircraft carrying the president of the United States.

From FAA Air Traffic Control document, Section 7.a:

Presidential aircraft and Presidential family aircraft:
When the President is aboard a military aircraft, state the name of the military service, followed by the word “One.”
EXAMPLE-
“Air Force One.”
“Army One.”
“Marine One.”


text:
Is it legal for a private pilot to "hold out" offering free passenger flights?
Is it legal for a private pilot to advertise that (s)he offers free passenger flights?

"Holding out" is relevant only in determining whether a flight is private carriage or common carriage, as described in AC 12-120. The definition of common carriage used by the FAA is:

a holding out of a willingness to
transport
persons or property
from place to place
for compensation

If you receive any compensation for these flights, you would fall under the definition of common carriage and this would be illegal. The FAA interprets "compensation" very broadly, including:

Reimbursement of expenses (e.g. fuel, oil, transportation, airport expenditures, aircraft rental fees, lodging, costs of ownership etc.)
A free meal
Logging of flight time when the pilot does not have to pay for the costs of operating the aircraft
Salary or wages
Goodwill in the form of expected future economic benefit

So you would need to be sure that you are not receiving any compensation. The passenger can't give you a tip or buy you dinner. They can't pay pro rata share of the expenses. If you have any business relations with your passengers in the future, you can expect them to fall under a great deal of scrutiny.
As long as you can avoid being compensated in any sense, this should be legal. Although I would be wary of doing so anyway, since the thought of having to fight the FAA in court over this should certainly give you pause. If this is something you are actually planning on doing, as opposed to just a thought experiment, it may be wise to consult with a lawyer before starting.

The passengers also can't dictate where to go and the pilot must have a reason to make the flight to that airport.  There are very interesting NTSB case decisions on the subject.  https://www.ntsb.gov/legal/alj/Pages/ONOQuery.aspx

"Goodwill is a form of prohibited compensation." https://www.ntsb.gov/legal/alj/OnODocuments/Aviation/5061.pdf

@wbeard52 "Goodwill is a form of prohibited compensation" is a shortened form of "Goodwill in the form of expected future economic benefit" above. If you continue on to the next paragraph, it is made clear that it is referring to the expectation of future concrete benefits that can reasonably be construed to come from goodwill.

@wbeard52 Do you have a source on your other claim? The passengers not be long allowed to dictate where you go is the case when the pilot and passengers are cost sharing, in order to take advantage of an
explicit exception to the prohibition against a private pilot receiving compensation. If the pilot is not receiving compensation at all I don't see how it should apply.

It seems the FAA has provided legal interpretations consistent with pro rata compensation for the flight.  I don't see any legal interpretations stating the passengers can dictate a destination if they don't pay the pro rata share.  It would be interesting to see what the FAA would say.  I can see both sides.  https://www.faa.gov/sites/faa.gov/files/faa_migrate/interps/2009/Bobertz-ANM7_2009_Legal_Interpretation.pdf

@wbeard52 It's quite clear, in my opinion. Everything that is not forbidden is permitted. Compensation is forbidden, subject to a whole mess of exceptions and exceptions to exceptions. Flying people where they want to go is not forbidden anywhere.

@wbeard52, the FAA is concerned with unregulated de-facto charter operators flying "under the radar". I don't think they really care if Bill suggests to pilot Steve that they fly somewhere for a burger on a sunny Saturday. However, if you want to request permission to go somewhere your friend recommends that wasn't your idea, please ask your local FSDO and report back here. I'd be curious to know what they say...


text:
Do cell phones interfere with GA avionics?
I think most people know that cell phone signals can interfere with airliner avionics; that's why airplane mode exists. Is this an issue with small GA planes?

What research have you done to find out?

You are mistaken. Cell phones are not banned onboard because they do interfere with airliner avionics. They are banned for two reasons:

because their use while airborne interferes with ground-based communications. This is an FCC rule, not an FAA rule, and has nothing to do with the aircraft and everything to do with the consequences on the ground. See FAA AC 91.21-1D, at 9.1 "Restricting Airborne Cellular Telephone Use," and 47 CFR §22.925.

because it is possible that certain portable electronic devices could interfere with aircraft navigation or communication systems. The FAA permits the operator of the aircraft to allow any portable electronic devices once they have determine that they in fact do not interfere with these systems. This is in CFR 14 §91.21 for Part 91 operations, and there are similar rules in Part 121, 125, and 135 operations. This same rule applies to most electronics- even in airplane mode and even if they do not intentionally transmit radio waves, the default rule is that they are not allowed. In practice, many operators allow them during at least some phases of the flight.

In short: any portable electronic device has the "potential" for interfering with aircraft systems. It appears that most of them, at least most of the time, do not do so significantly. Occasional reports of possible PED interference have proven rare and difficult to replicate. See for example this and appendix I in this document.
Regardless of any interference with aircraft systems, cell phones in particular are forbidden by the FCC any time you are airborne.

The one phenomenon I've observed flying when an active cell phone is nearby (like my own phone) is that distinctive "D-D-D-D-D-D-D-D-D" sound that comes over the comms audio, which I believe happens when the phone is in communication with a tower. Mildly annoying but otherwise no big deal.

@JohnK That is mildly annoying but usually not dangerous. More concerning is interference with, say, VOR or ILS, which may just give wrong information. Particularly 2G communications radiate a lot at around 217 Hz, which is uncomfortably close to the 90 and 150 Hz sideband frequencies used in the ILS localizer. Newer phones make do with much less total power radiated so presumably the interference problems are smaller.

I've noticed that my Garmin Etrex handheld GPS makes an audible noise over the speaker of a handheld aviation radio when they are close together.

As I understand it, the use of radio transmitting devices (that aren't permanently installed) is generally prohibited in commercial aircraft because the crew have very little control over them.  In the case of a small GA aircraft this would be far less of a problem, as the pilot could easily ask their passenger to desist using the device if there were a problem.

@Frog Radio-transmitting devices are very commonly allowed. Wifi and bluetooth devices, for instance. On a commercial flight, the crew can (and has) ask passengers to turn off their devices if required.

@Chris - hence the qualified 'generally prohibited'.  For completeness, Bluetooth and to some extent Wifi are permitted because of the limited power (typically 100mW, can be much less) and the relatively narrow band that they use, in contrast with cellphones that can transmit several watts (and likely will do when in the air) and over many frequency bands (450MHz to 2.5GHz and beyond).

@Frog Most of the documented interference issues with PEDs appear to be from devices that were spuriously emitting radio waves in a part of a spectrum they weren't designed to to begin with. A properly-operating cellphone, like a properly-operating wifi device, shouldn't interfere with aircraft systems. It's when the device is operating incorrectly that is the problem: it can take very little power of spurious emissions in the wrong part of the spectrum to cause harmful interference.

The FAA also makes it clear that the reason it is not considering allowing cell phones in aircraft is an FCC rule.

@Chris (I’m mindful not to get into extended discussion) and yet there’s significant concern about well-behaved 5G towers interfering with aircraft radar, not because the towers are transmitting out-if-band but because the radars have so little discrimination.


text:
Can a helicopter autorotate from a hover?
If a hovering helicopter's engine fails, can the helicopter autorotate as it could if it were moving?

@757toga no, I hadn't thought of that. I'm interested in theoretical possibility more than practicality, so assume there is enough altitude for any maneuvers to be made.

Vertical autorotation is not a good idea

Look up the 'Dead Man's Curve' for a helicopter.  It gives the zones for safe flying (in event of engine failure) as a function of speed and altitude.  Hover is the left-side of the curve (where V=0).
Very low, a helicopter can safely hover and have an engine failure -- from low altitude, it won't pick up enough speed to have terrible consequences when it reaches the ground.
Up high, a helicopter has enough altitude to use that potential energy to safely autorotate.
There is a region of altitudes in-between where the helicopter can not safely hover in the event of an engine failure.

Wow, I've never seen this diagram, that's very insteresting. Is that the reason why helicopter don't take off and land vertically (except for the last bit) but basically follow some kind of "glide slope" (in lack of a better term)?

@kruemi Yes it is.  It is also the reason you usually don't see helicopters hovering at altitude (also lower fuel consumption) -- or example a Police or News helicopter will usually orbit the point of interest instead of hover at a single vantage point.

The helicopter will be able to maintain rotor speed using the same "windmill" effect.  However, unless the autorotation is initiated just slightly above the ground, the descent rate will become too large to be survivable (and control may be lost due to vortex ring state).
If the helicopter is moving too slow (KTAS < 50), but is above the H-V curve in altitude, the pilot would accelerate to a survivable autorotation speed where (1) the rate of descent will be smaller, (2) range will hopefully allow the pilot to find a suitable landing spot, and (3) forward speed will be used to boost lift and rotor speed in the flare, just before landing.
A pilot should be aware of many airspeeds related to this: (1) the minimum airspeed to use in autorotation, (2) the speed that will provide the minimum descent rate in autorotation, (3) the speed that will provide max range in autorotation and (4) the max speed in autorotation.

Yes it could, because the process of auto-rotation does not rely on the forward motion. Think of auto-rotation as gliding, but in a helical path.
A glider has to constantly descend¹ to maintain airspeed - when descending, a component of its weight counters the drag. This allows the plane to stay in motion, thereby maintaining the airflow needed by the wing to produce lift.
In a helicopter, this wing rotates while descending, and is called a 'rotor'. Other than this difference, the mechanics are identical to that in gliding. Since the blades follow a helical path, a component of helicopter's weight opposes the "drag" (or torque) of the rotor.
This allows the rotor to maintain its rotation speed, providing the blades the airflow they need to produce lift. Since blades don't rely on forward motion of the helicopter to produce this lift, auto-rotation is perfectly possible without forward motion.

¹The glider must constantly descend relative to the ambient air, not necessarily relative to the ground.

I think this answer misses the point. Forward speed helps immensely during the landing flare. As forward speed bleeds off, it adds energy to the rotor (just like an autogyro) and that energy can be used to arrest the vertical descent. While you can autorotate without forward speed, you will impact the ground without much flare.

@RainerP. You are right, but OP just asked if it was theoretically possible to have auto-rotation without forward speed; he didn't mention anything about landing.


text:
At what point is the input data to glass cockpit PFDs converted to digital?
At a very basic level, primary flight displays take data from sensors, do calculations, and display the results on a screen. Of course, because they are digital computers, the input must be digital, at least inside the processor. However, the values being measured, such as air pressure, airspeed, etc., are fundamentally analog, so there must be analog sensors involved. At what point is the analog data from the sensors converted to digital data for the computer?

Glass cockpits are modular systems, and not all of them are exactly the same. But many/most include a module called an Air Data Computer (ADC) which performs the digitalization function for the parameters you mentioned (air pressure [= altitude] and airspeed). This is a self-contained module installed in the aircraft. It will have pneumatic connections for the actual sensors on the airframe, and some form of digital output, like an ARINC 429 data bus connected to other modules in the system like the displays. Sometimes the digital data first goes through another module like an I/O concentrator before it reaches the displays.
For a concrete example, this particular Garmin G1000 system digitizes air data using a GDC 74A air data computer:

The installation manual for the GDC 74A shows its pneumatic connections:

Other modules like Attitude/Heading Reference Systems (AHRS) perform similar digitization and filtering functions for signals from sources like magnetometers and accelerometers for aircraft orientation or rates. Many systems have several other types of modules, or in-sensor digitization, for radio altimeters, flight control servos, etc. etc.

Conveniently then, the Air Data Computer contains the Analogue-to-Digital Converters (which in most other contexts is what the initials ADC would normally standard for). :)

On smaller aircraft, the conversion is done within the Air Data Computer (see TypeIA's answer). This makes replacing older steam gauges with a glass cockpit relatively simple because you just send the existing pitot/static lines to the ADC instead of the instruments directly.
On lager airliners, which were designed with a glass cockpit from the beginning, you typically want to do the conversion to digital data earlier. This avoids having several long pitot and static lines going through the entire aircraft, which saves weight. For example, on the Airbus A320 only the standby instruments have direct pitot and static lines. Everything else is converted to digital data in Air Data Modules earlier:

The system includes [...] eight ADMs (Air Data Modules) which convert pneumatic data from PITOT and STAT
probes into numerical data for the ADIRUs. [...]
Probes Schematic

(Airbus A320 FCOM - Navigation - ADIRS)
I think on newer A320 variants, which use the digital Integrated Standby Instrument System (ISIS), they also removed these pitot and static lines and use the ADM data directly, but I couldn't find a reference to confirm this.


text:
Can a student pilot certificate be used for transportation with an endorsement?
If I live in Anytown and need to make a trip over to Bigcity for non-flight-training-related purposes, I have a student pilot certificate, it's just me going, and I have a solo endorsement from my instructor, is this legal? In other words, are solo flights made by student pilots for a primary purpose other than flight training legal?

When you are a student pretty much any flight is flight training.

That would be considered a cross-country solo flight.
The flight will have to be conducted within the limitations set forth in §61.89.
You must possess the following endorsements to make the flight:

A valid solo endorsement in the proposed make and model of aircraft (§61.87).

A night flight endorsement (if applicable) (§61.87).

A specific endorsement for each proposed cross country flight (§61.93(c)(d)), or, if the cross country flight meets the terms of §61.93(b), specific endorsement to make repeated cross country flights to and from their home airport to a specific airport within 25 nm of their home airport.

If the airport lies within class B airspace, a specific endorsement to operate in that specific bravo airspace (§61.95 (a), (b)).

If you are seeking a Sport or Recreational Pilot Certificates, and you want to fly into a towered airport for a destination, you will need an endorsement to operate from that specific airport in that specific Class B, C, or D airspace (§61.94).

I’m not sure what the term “transportation” means in the title, but about the only thing you can transport on that flight is your little pink body, and that cannot be done so for reasons of in furtherance of a business - see the rules in §61.89(a)(1 thru 4).
Aside from that, if you meet all those requirements and your instructor signs off on it, you can certainly make the flight!

Hmm. The whole point of the question is .. "need to make a trip.." for "non-flight-training purposes".  Hence for (say) a wedding or meeting or shopping.

It depends on the circumstances. Parts 61.89 and 61.93 describe the limitations. In particular, a student pilot cannot fly in furtherance of a business. So flying yourself to a business meeting is no good but flying yourself to a wedding is probably fine.
It should go without saying that all the other requirements still apply. In particular, you need to have an appropriate endorsement. Solo endorsements are given for specific airport pairs or routes, and are not permission to go wherever you want whenever you want.

It seems hard to believe that wedding is legal but meeting not.  Say I'm a human "on the ground".  It's equally dangerous to me if he's going to a wedding or a meeting. You see?

@Fattie It doesn't matter if you think it makes sense. Doing anything in furtherance of a business as a student pilot is explicitly forbidden in §61.89(a)(4).

Hi Chris, you may misunderstand me 180.  Of course, he should not be allowed to go to a business meeting.  Similarly, he should not be allowed to go to a wedding.

@Fattie It's just as dangerous to you, a person on the ground, whether they are going for a wedding or are doing it for flight training.

The purpose of the law seems to be that you can fly as a learner/novice, only when, you're doing nothing other than literally learning, practicing, with no other goals, aims, distractions, pressures, issues. Assuming that is the point or purpose of the law, I'd assume that bot "personal business" (weddings) and "business business" (meetings) are outlawed.

@Fattie That's not what the law says, though. If that was the intention of the law, they would have written it that way.

Chris, yes you're totally correct. The law is the law.


text:
How do IFR flights in IMC in Class G airspace not collide?
According to Wikipedia, in Class G airspace, "Operations may be conducted under IFR or VFR. ATC has no authority but VFR minimums are to be known by pilots. Traffic Information may be given as far as is practical in respect of other flights."
How do IFR flights in IMC in Class G airspace not collide with each other?

Related-- https://aviation.stackexchange.com/q/79262/34686, https://aviation.stackexchange.com/q/21888/34686, https://aviation.stackexchange.com/q/47569/34686, https://aviation.stackexchange.com/a/45324/34686, https://aviation.stackexchange.com/q/1368/34686

As a controller, I am required to separate the two IFR arrivals landing at the same uncontrolled airport. If i understand the OP's question correctly, this scenario should NEVER happen unless the controller has made a fundamental mistake.

IFR airplanes are expected to coordinate with each other if two airplanes arrive to shoot an approach at the same time in uncontrolled airspace.  Whomever arrives first is going to be announcing their intentions per the reporting requirements, and someone following, if they are that close behind and could have a conflict, will have to figure out an appropriate way to delay their arrival, such as holding at a fix. There's nobody to tell you what to do, so you just use common sense.
The key thing is the requirements are to report your arrival, and your progress at specific stages in the approach, and if you are sharing airspace with another IFR flight arriving at the same time (pretty rare), you coordinate your actions to stay out of each other's way in the same way you would if you were VFR.

What frequency is used? The CTAF? What if they're in cruise flight, not shooting an approach?

An airport in uncontrolled airspace that has an instrument approach will have a Mandatory Frequency that is to be used for all flights.  The MF will be shown on the approach chart. It may be a unique frequency, or it may be a Unicom or regional Aeradio frequency. If an airport has an MF you must broadcast your intentions whether VFR or IFR.

You seem to be answering the question with a USA-centric bent. In the USA it is exceedingly rare for Class G to extend higher than 1200' AGL, which all-but-precludes IMC flight, per 14 CFR 91.119(a); thus the most common scenario for two IFR aircraft to meet in Class G is at an airport. In other parts of the world Class G is much more extensive and @Someone's question is not so easily answered.

I'm in Canada, where uncontrolled IFR is common in the North.

(Re-posting to make a correction) -- I don't think we have the Manditory Frequency concept in the US. I learned to fly (power) at an airport, with instrument approaches, that was Class G below 700' AGL, and I learned in a plane with no radio. (Actually I could receive but not transmit, but that's not really germane to the point.) Obviously I only flew when conditions were VFR. Are planes without radios allowed to fly at airports with Manditory Frequencies listed, in VFR conditions, in Canada?

Yes you are allowed to operate NORDO at an MF airport.

Ideally, all aircraft will be giving position reports on CTAF (which does exist for en route in some places) and will self-deconflict.
Where CTAF does not exist, or if pilots choose not to use it, then worst case we're relying on Big Sky Theory.

Does "big sky theory" mean "the sky is big, so there probably aren't two planes in the same place"? That doesn't sound like a good idea to rely on

@Someone-OnStrike That's exactly what it means, and unless you're low near an airport, it's surprisingly effective.  The sky is very big, and planes are very small.